Typically, solid oxide fuel cells (SOFC) employ an electrolyte of ion-conductive oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (MEA). The electrolyte electrode assembly is interposed between a pair of separators (bipolar plates). In use, generally, a predetermined numbers of the separators and the electrolyte electrode assemblies are stacked together to form a fuel cell stack.
In the fuel cell stack of this type, when flat plate stack type solid oxide fuel cells are used, it is required to reliably position the fuel cells relative to each other in the stacking direction. For this purpose, in a fuel cell stack disclosed in Japanese Laid-Open Patent Publication No. 2003-086232 (hereinafter referred to as the conventional technique 1), as shown in FIG. 11, end plates 1a are provided at both ends of the fuel cell stack in the stacking direction. Insulating plates 2a and current collection plates 3a are provided inside the end plates 1a, and a stack body formed by stacking MEAs 4a and separators 5a alternately is sandwiched between the current collection plates 3a. 
At the time of producing the fuel cell stack, components of the fuel cell stack are stacked successively such that end surfaces of respective components of the fuel cell stack are aligned to a plurality of positioning guides 7a of an assembling jig 6a. Then, a pair of end plates 1a are fixed together using bolts (not shown) to apply a tightening load to the fuel cell stack in the stacking direction.
Further, in a method of assembling a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2005-079024 (hereinafter referred to as the conventional technique 2), as shown in FIG. 12, pin holes 2b are formed at four corners and intermediate portions in respective sides of a separator 1b as a component of the fuel cell. Then, pins 3b provided in a jig (not shown) are inserted into the pin holes 2b to position the separator 1b. 
Further, as shown in FIG. 13, a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2007-179935 (hereafter referred to as the conventional technique 3) includes a stack 1c formed by stacking stack components including rectangular cells. A first cutout portion 2c extending in the stacking direction of cells is formed in a first side wall of the stack 1c, and a second cutout portion 3c extending in the stacking direction of the cells is formed in a second side wall of the stack 1c opposite to the first side wall. As viewed from a direction perpendicular to the first side wall, the first cutout portion 2c and the second cutout portion 3c are not overlapped with each other.
Cylindrical guide shafts (not shown) contact the first cutout portion 2c and the second cutout portion 3c of the end plate to position the end plate. Then, an insulator is stacked on the end plate. Then, a terminal is provided on the insulator, unit cells are provided on the terminal, another terminal is provided on the unit cells, another insulator is provided on the terminal, and another end plate is provided on the insulator successively in the same manner.